Pore Pressure Prediction Based on High Resolution Velocity Inversion in Carbonate Rocks, Offshore Sirte Basin Ͳ Libya*
Robert M. Gruenwald1, Javier Buitrago2, Jack Dessay2, Alan Huffman3, Carlos Moreno3, Jose Maria Gonzalez Munoz2, Carlos
Diaz2 and Khaeri Segayer Tawengi
Search and Discovery Article #40551 (2010) Posted June 30, 2010
*Adapted from oral presentation at AAPG Annual Convention and Exhibition, New Orleans, Louisiana, April 11-14, 2010 1Exploration, REMSA, Tripoli, Libyan Arab Jamahiriya ([email protected]) 2Exploration, REMSA, Tripoli, Libyan Arab Jamahiriya 3Fusion Petroleum Technologies Inc., Houston, TX
Abstract ResidualTM velocity analysis was employed to refine the input gathers and velocity field for pressure prediction in Cretaceous carbonates and further processed to produce an inverted velocity cube. From the acoustic inversion a shale velocity trend was generated and used for pressure calibration with the control wells to predict pressures in 3D. Attributes were generated for pore pressure (PP), pore pressure gradient (PPG), overburden pressure (OB), overburden gradient (OBG), fracture pressure (FP), fracture pressure gradient (FPG) and effective stress (ES). Two reservoirͲspecific PP models with different saturating fluids were generated to account for buoyancy effects; Z Reservoir = FG at structural crest. From down dip pressures PͲMax is calculated to a maximum extent of the possible fluid column to predict for pore fill columns using the local closure and spill points and pressure prediction at the penetration point for the reservoir assuming the existence of a centroid pressure point in a monoclinal structure. Fluid gradients used were; for brine 0.465 psi/ft, for light oil 0.3 psi/ft and for gas 0.1 psi/ft. PPP results indicate a benign shallow section and then increases steadily below 11,500 ft to a maximum of 15.5 PPG at 15,100 ft and temperatures exceeding 300 deg F at TD. Comparison of preͲdrill prediction, based on seismic velocities, with LWD guided pressure monitoring, intermediate and final VSP data and final WL results show a high affinity with the prognosis. Space and resolution dependent PP Models can be generated from actual well data and seismic displaying the inherent velocity heterogeneity of seismic data versus high resolution of WL data.
Integration of regional knowledge, sound understanding of the basin specific structural setting and offset well data, PSTM and PSDM data, with realͲtime drilling parameter monitoring and a technology limited by the carbonate setting, provides valuable data for kick management and casing design in a HPHT environment.
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Pore Pressure Prediction based on High Pore Pressure Prediction based on High Resolution Velocity Inversion in Carbonate Resolution Velocity Inversion in Carbonate
Javier Javier BuitragoBuitrago*, Jack *, Jack DessayDessay*, Carlos Diaz*, Robert *, Carlos Diaz*, Robert GruenwaldGruenwald*, *, Alan HuffmanAlan Huffman**, Carlos Moreno**, Jose Maria Gonzalez **, Carlos Moreno**, Jose Maria Gonzalez MuMuññozoz*, *,
KhaeriKhaeri SegayerSegayer TawengiTawengi******
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Mud Losses encounter on the well B1NC152 at 371 ft
In the Cenomanian, PP Increase is expected at 13000 ft (PP= 12.1 ppge) and later at 15000 ft (PP = 14.2 ppge) in the Albian reservoir level (corr. with B1NC152)
Mud Losses expected at 8800 to 9400 ft (corr with well A1NC173)
Mud Losses encounter on the well A1NC120 from 560 to 1369 feet
Presenter’s Notes: Offset Well Information
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Offset pressure data from the NC 120-A1 (purple and magenta) and NC 173-A1 (blue) wells that had seismic data support
Offset wells: Pressures from MW
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Velocity to effective stress calibration using a hybrid model (red curve) that moves from the minimum fluid pressure model at low effective stress to the maximum fluid pressure model at high effective stress.
Offset wells: Effective stress vs. Velocity
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Pressure Gradient Data (ppg)
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8.00 10.00 12.00 14.00 16.00 18.00 20.00
Dep
th (f
bsl)
S-45
S-32S-26
S-24
Revised prediction removal of initial pressure ramp, but honoring the major deep pressure ramp
Pre-Drill Prediction vs. Drilling Calibration
Presenter’s Notes: Plan was to predict first abnormal regime, result is lower pressure (losses).1. Isolate the first “predicted” abnormal pressure regime (Cased off Loss Zone)2. Drill safely the sharp pressure ramp towards the HP zoneHere it has to be mentioned that 12772 MDT point was taken after killing the well at TD.
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Pressure Gradient Data (ppg)
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8.00 10.00 12.00 14.00 16.00 18.00 20.00
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S-45
S-32S-26
S-24
Revised prediction removal of initial pressure ramp, but honoring the major deep pressure ramp
Pre-Drill Prediction vs. Drilling Calibration
The plan
1. Isolate the first “predicted” abnormal pressure regime (Cased off Loss Zone)
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Pressure Gradient Data (ppg)
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S-45
S-32S-26
S-24
Revised prediction removal of initial pressure ramp, but honoring the major deep pressure ramp
Pre-Drill Prediction vs. Drilling Calibration
2. Drill safely the sharp pressure ramp towards the HP zone
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Pressure Gradient Data (ppg)
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Pre-Drill Prognosis with drilled under / over pressure ramp
Pre-Drill Prediction vs. Drilling Calibration
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Pressure Gradient Data (ppg)
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14000
16000
18000
8.00 10.00 12.00 14.00 16.00 18.00 20.00
Dep
th (f
bsl)
S-45
S-32S-26
S-24
Revised prediction removal of initial pressure ramp, but honoring the major deep pressure ramp
Pressure Gradient Data (ppg)
0
2000
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8.00 10.00 12.00 14.00 16.00 18.00 20.00
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th (f
bsl)
Pre-Drill Prognosis with drilled under / over pressure ramp
Pre-Drill Prediction vs. Drilling Calibration
Original prediction from pre-drill location with actual drilling data including drilled MW (blue), PreView data (red) and MDT data (green). The MDT at 12,772’ is likely to be supercharged (SLB final)
2121
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
PSDM Interpretation (Available Post-Drill)
13500’
11250’
10500’
10000’
10250’
High VelocityInterval
S32Santonian Unconf.
S26 Cenomanian
S24 Albiian
TD
BMSL
13625’
11375’
10625’’
10125’
10375’
MD
S50 Kheir 8413 (BMSL) 8530 MD
Sabil 8755 (BMSL) 8880 MD
S45 BTU 9965 (BMSL) 10090 MD
Losses Zone 1 from 8750 ft – 8819 ft
Losses Zone 210010ft – 11340ft
Presenter’s Notes: PSDM Line across Well Location
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Lessons Learned Geopressure issues
Presenter’s Notes: The well did not kick at the 12772’ MDT point because it is likely laterally connected to a reservoir “isolated centroid”, or connected by fracture deeper part of the reservoir like a short circuit but disconnected from shale behavior
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Severe to totallosses
Lessons Learned Geopressure issues
MDT P/EMW 15.13 ppg
“after killing well at TD
MW 16 ppg”BGG decreased after
MW increase
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Calibration panel (right) showing the actual MW data (blue), the SLB PreView data (orange) and the MDT data (cyan) for the well and the original predicted pressure gradient (green curve). The left panel is the seismic shale velocities. These are for the original predicted location. Datum is mudline.
“Original Location” Geopressures – Post drilling
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Calibration panel (right) showing the actual MW data (blue), the SLB PreView data (orange) and the MDT data (cyan) for the Barracuda well and the predicted pressure gradient (green curve) for the actual location where the well was
drilled. The left panel is the seismic shale velocities. Datum is mudline.
“Final Drilled Location” Geopressures – Post drilling
Note milder shallow ramp
Presenter’s Notes: This is the velocity function from the actual drilled location, which is 250 meters from the original prediction location. Note the decreased shallow ramp behavior. This velocity function predicts a lower pressure at 9,000 to 10,000 feet than the original location. Green curve on right with half ppgerror bar final location prediction
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Calibration panel (right) showing the actual MW data (blue), the SLB PreView data (orange) and the MDT data (cyan) for the well and the predicted pressure gradient (green curve). The left panel is the Vp from the VSP inversion. The minima on the sonic curve are the shaley zones. Datum is mudline.
“Final VSP” Geopressures – Post drilling
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Inverted Vp at Well – Cretaceous Section
1000 2000 3000 4000 5000 6000 7000
m/s
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
Comparison of velocity data from the well sonic log, VSP and VSP inversion. The magenta curve is the shale minima trend from the check shot survey.
Comparison Int. VSP vs. Final VSP
Presenter’s Notes: Mnemonic naming description;1st TRACKCstk_inv = Corridor stack inversion from the intermediated (1st) run checkshotCstk_shl= Low frequency shale trend velocityVint_flt= Checkshot interval velocityVP_ED= Velocity derived from the sonic logPSTMVint= inverted velocity constrained by ThinMAN2nd TRACKMeasured Depth3rd TRACKVP_ED= Velocity derived from the sonic logPSTMVint=inverted velocity constrained by ThinMANVP2chkin=Corridor stack inversion from the final (TD) run checkshotVP2chkst=Checkshot interval velocity from the final (TD) run checkshotPSTMVint= inverted velocity constrained by ThinMAN
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AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
AAPG Annual Convention & Exhibition – 11-14 April New Orleans R. Gruenwald & Alan R. Huffman PhD
ConclusionIntegration of regional knowledge, sound understanding of the basin specific structural setting and offset well data, PSTM and PSDM data, with real-time drilling parameter monitoring and a technology limited by the carbonate setting, provides valuable data for kick management and casing design in a HPHT environment.
Pressure Prediction Can Be Performed In Complex Geologic Environments Under The Right Conditions
Successful Predictions Require The Following:
Robust Velocities That Can Be Relied Upon To Indicate Presence of Pressure Anomalies
Investigate Thoroughly The Effects of Lithology on Velocity
Good Understanding Of Lithological and Depositional Variability
Sufficient Offset Well Calibration To Determine Which Pressure Mechanisms Are Active In A Study Area
Routine to Distinguish Poor Offset Well Data Adding Negative Bias (A1-NC173) from Valid Offset Well Data
Appropriate Seismic Methods Designed To Resolve Changes in Velocity Related To Pore Pressure
Ability to Detect Velocity Variations in Complex Lithological Settings
Full Integration of Structural, Stratigraphic and Geophysical Inputs
Pre-Drill Predictions are designed to predict shale pressures ahead of the bit. Open fracture systems can cause the pre-drill prediction to be in error because of vertical fluid migration across formations. Wide-azimuth data are required to detect these fracture systems pre-drill.
